Loss of immune tolerance to IL-2 in type 1 diabetes.

Type 1 diabetes (T1D) is characterized by a chronic, progressive autoimmune attack against pancreas-specific antigens, effecting the destruction of insulin-producing ß-cells. Here we show interleukin-2 (IL-2) is a non-pancreatic autoimmune target in T1D. Anti-IL-2 autoantibodies, as well as T cells specific for a single orthologous epitope of IL-2, are present in the peripheral blood of non-obese diabetic (NOD) mice and patients with T1D. In NOD mice, the generation of anti-IL-2 autoantibodies is genetically determined and their titre increases with age and disease onset. In T1D patients, circulating IgG memory B cells specific for IL-2 or insulin are present at similar frequencies. Anti-IL-2 autoantibodies cloned from T1D patients demonstrate clonality, a high degree of somatic hypermutation and nanomolar affinities, indicating a germinal centre origin and underscoring the synergy between cognate autoreactive T and B cells leading to defective immune tolerance.

Materno-Fetal Transfer of Preproinsulin Through the Neonatal Fc Receptor Prevents Autoimmune Diabetes.

The first signs of autoimmune activation leading to ß-cell destruction in type 1 diabetes (T1D) appear during the first months of life. Thus, the perinatal period offers a suitable time window for disease prevention. Moreover, thymic selection of autoreactive T cells is most active during this period, providing a therapeutic opportunity not exploited to date. We therefore devised a strategy by which the T1D-triggering antigen preproinsulin fused with the immunoglobulin (Ig)G Fc fragment (PPI-Fc) is delivered to fetuses through the neonatal Fc receptor (FcRn) pathway, which physiologically transfers maternal IgGs through the placenta. PPI-Fc administered to pregnant PPIB15-23 T-cell receptor-transgenic mice efficiently accumulated in fetuses through the placental FcRn and protected them from subsequent diabetes development. Protection relied on ferrying of PPI-Fc to the thymus by migratory dendritic cells and resulted in a rise in thymic-derived CD4(+) regulatory T cells expressing transforming growth factor-ß and in increased effector CD8(+) T cells displaying impaired cytotoxicity. Moreover, polyclonal splenocytes from nonobese diabetic (NOD) mice transplacentally treated with PPI-Fc were less diabetogenic upon transfer into NOD.scid recipients. Transplacental antigen vaccination provides a novel strategy for early T1D prevention and, further, is applicable to other immune-mediated conditions.

Short-term subcutaneous insulin treatment delays but does not prevent diabetes in NOD mice.

Despite encouraging results in the NOD mouse, type 1 diabetes prevention trials using subcutaneous insulin have been unsuccessful. To explain these discrepancies, 3-week-old NOD mice were treated for 7 weeks with subcutaneous insulin at two different doses: a high dose (0.5 U/mouse) used in previous mouse studies; and a low dose (0.005 U/mouse) equivalent to that used in human trials. Effects on insulitis and diabetes were monitored along with immune and metabolic modifications. Low-dose insulin did not have any effect on disease incidence. High-dose treatment delayed but did not prevent diabetes, with reduced insulitis reappearing once insulin discontinued. This effect was not associated with significant immune changes in islet infiltrates, either in terms of cell composition or frequency and IFN-γ secretion of islet-reactive CD8(+) T cells recognizing the immunodominant epitopes insulin B(15-23) and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)(206-214). Delayed diabetes and insulitis were associated with lower blood glucose and endogenous C-peptide levels, which rapidly returned to normal upon treatment discontinuation. In conclusion, high- but not low-dose prophylactic insulin treatment delays diabetes onset and is associated with metabolic changes suggestive of ß-cell "rest" which do not persist beyond treatment. These findings have important implications for designing insulin-based prevention trials.

acDCs enhance human antigen-specific T-cell responses.

Detection of human Ag-specific T cells is limited by sensitivity and blood requirements. As dendritic cells (DCs) can potently stimulate T cells, we hypothesized that their induction in PBMCs in situ could link Ag processing and presentation to Ag-specific T-cell activation. To this end, unfractionated PBMCs (fresh or frozen) or whole blood were incubated for 48 hours with protein or peptide Ag together with different DC-activating agents to rapidly and sequentially induce, pulse, and mature DCs. DC activation was therefore lined up with Ag recognition by neighboring T cells, thus telescoping the sequential steps of T-cell activation. Efficient processing of protein Ags made prior knowledge of epitopes and HLA restrictions dispensable. While reducing stimulation time, manipulation and blood requirements, in situ DC induction specifically amplified Ag-specific T-cell responses (cytokine secretion, proliferation, CD137/CD154 up-regulation, and binding of peptide-HLA multimers). IL-1ß, although released by DCs, was also secreted in an Ag-specific fashion, thus providing an indirect biomarker of T-cell responses. These accelerated cocultured DC (acDC) assays offered a sensitive means with which to evaluate T-cell responses to viral and melanoma Ag vaccination, and may therefore find application for immune monitoring in viral, tumor, autoimmune, and transplantation settings.

Autoimmunity during thymectomy-induced lymphopenia: role of thymus ablation and initial effector T cell activation timing in nonobese diabetic mice.

Autoimmune diseases develop in selected normal mouse strains when thymectomy (Tx) is performed at 3 days of age (d3-Tx). Insufficient T cell regulation after Tx may result from a defect in regulatory T (Treg) cells or from an augmented effector T (Teff) cell number/pathogenicity. We have previously shown that Tx at 3 wk (wk3-Tx), the age of massive islet Ag release, accelerates diabetes onset. We now have determined diabetes incidence in d3-Tx nonobese diabetic mice and compared the frequency and function of their Teff and Treg cells with those of wk3-Tx mice. We found that d3-Tx had no effect on diabetes incidence, but induced gastritis. After day 3 and week 3 Tx, Treg cells were fully competent and their frequency increased. The number of diabetogenic T cells was greatly amplified after wk3-Tx and likely overcame Treg cell control, leading to an early tolerance breakdown. By contrast, in d3-Tx mice, activation concerned few cells and Teff cell amplification remained controlled. This suggests that Tx enhances autoimmunity when it coincides with the first encounter of autoreactive T cells with their cognate Ag. The relationship between Tx-induced lymphopenia, tissue remodeling, and autoimmunity is discussed.

Lymphopenia-induced spontaneous T-cell proliferation as a cofactor for autoimmune disease development.

Lymphopenia is thought to be a major cause of tolerance breakdown. In a lymphopenic environment, self-recognition events induce some T cells to expand strongly (a mechanism known as spontaneous proliferation). In this study, we show that in C57BL/6 mice, the repertoire resulting from lymphopenia-induced spontaneous CD4(+) T-cell proliferation included a proportion of regulatory T cells as large as that observed in a normal mouse, and no autoimmune disorder was observed. By contrast, in nonobese diabetic mice, differences in the ability of conventional and regulatory T cells to expand in response to lymphopenia led to an unbalance between these 2 T-cell compartments at the expense of regulatory T cells, resulting in the onset of autoimmune diseases. Notably, this accounted for the rapid transfer of diabetes with small numbers of BDC2.5 CD4(+) T cells. Thus, lymphopenia does not itself induce autoimmunity, but it should be considered as a cofactor for the development of autoimmune disorders.

Influence of a non-NK complex region of chromosome 6 on CD4+ invariant NK T cell homeostasis.

The number and function of immunoregulatory invariant NKT (iNKT) cells are genetically controlled. A defect of iNKT cell ontogeny and function has been implicated as one causal factor of NOD mouse susceptibility to type 1 diabetes. Other factors of diabetes susceptibility, such as a decrease of regulatory T cell function or an increase in TLR1 expression, are corrected in diabetes-resistant Idd6 NOD.C3H 6.VIII congenic mice. Thus, we surmised that the iNKT cell defects found in NOD mice may also be rescued in congenic mice. Unexpectedly, we found, in both the thymus and the periphery, a 50% reduction in iNKT cell number in NOD.C3H 6.VIII mice as compared with NOD mice. This reduction only affected CD4(+) iNKT cells, and left the double negative iNKT cells unchanged. In parallel, the production of IL-4 and IFN-gamma following alpha-GalCer stimulation was proportionally reduced. Using three subcongenic strains, we have narrowed down the region controlling iNKT development within Idd6 (5.8 Mb) to Idd6.2 region (2.5 Mb). Idd6 region had no effect on NK cell number and in vivo cytotoxic activity. These results indicate that the role of iNKT cells in diabetes development is equivocal and more complex than initially considered. In addition, they bring strong evidence that the regulation of CD4(+) iNKT cell production is independent from that of DN iNKT cells, and involves genes of the Idd6 locus.

The diabetes type 1 locus Idd6 modulates activity of CD4+CD25+ regulatory T-cells.

The genetic locus Idd6 confers susceptibility to the spontaneous development of type 1 diabetes in the NOD mouse. Our studies on disease resistance of the congenic mouse strain NOD.C3H 6.VIII showed that Idd6 influences T-cell activities in the peripheral immune system and suggest that a major mechanism by which the Idd6 locus modifies diabetes development is via modulation of regulatory T-cell activities. Our transfer experiments using total splenocytes and purified T-cells demonstrated that the locus specifically controls the efficiency of disease protection mediated by the regulatory CD4(+)CD25(+) T-cell subset. Our data also implicate the Idd6 locus in controlling the balance between infiltrating lymphocytes and antigen-presenting cells within the pancreatic islet.

Pancreatic lymph nodes are required for priming of beta cell reactive T cells in NOD mice.

Nonobese diabetic (NOD) mice develop spontaneous autoimmune diabetes that results from the destruction of insulin secreting beta cells by diabetogenic T cells. The time and location of the encounter of autoantigen(s) by naive autoreactive T cells in normal NOD mice are still elusive. To address these issues, we analyzed diabetes development in mice whose spleen or pancreatic lymph nodes (panLNs) had been removed. Excision of panLNs (panLNx) at 3 wk protected mice against insulin autoantibodies (IAAs), insulitis, and diabetes development almost completely, but had no effect when performed at 10 wk. The protection afforded by panLNx at weaning was not due to modifications of the immune system, the absence of autoreactive T cells, or the increase in the potency of regulatory T cells. That panLNs are dispensable during adult life was confirmed by the capacity of 10-wk-old panLNx irradiated recipients to develop diabetes upon transfer of diabetogenic T cells. In contrast, splenectomy had no effect at any age. Partial excision of mesenteric LN at 3 wk did not prevent accelerated diabetes by cyclophosphamide as panLNx did. Thus, in normal NOD mice, autoreactive T cell initial priming occurs in LNs draining the target organ of the disease from 3 wk of age.